The Current Transformer (C.T.), is a type of “instrument transformer” that is designed to produce an alternating current in its secondary winding which is proportional to the current being measured in its primary.
Current transformers reduce high voltage currents to a much lower value and provide a convenient way of safely monitoring the actual electrical current flowing in an AC transmission line using a standard ammeter. The principal of operation of a basic current transformer is slightly different from that of an ordinary voltage transformer.
Unlike the voltage or power transformer, the current transformer consists of only one or very few turns as its primary winding. This primary winding can be of either a single flat turn, a coil of heavy duty wire wrapped around the core or just a conductor or bus bar placed through a central hole.
Due to this type of arrangement, the current transformer is often referred to as a “series transformer” as the primary winding, which never has more than a very few turns, is in series with the current carrying conductor supplying a load.
The secondary winding however, may have a large number of coil turns wound on a laminated core of low-loss magnetic material. This core has a large cross-sectional area so that the magnetic flux density created is low using much smaller cross-sectional area wire, depending upon how much the current must be stepped down as it tries to output a constant current, independent of the connected load.
The secondary winding will supply a current into either a short circuit, in the form of an ammeter, or into a resistive load until the voltage induced in the secondary is big enough to saturate the core or cause failure from excessive voltage breakdown.
Unlike a voltage transformer, the primary current of a current transformer is not dependent of the secondary load current but instead is controlled by an external load. The secondary current is usually rated at a standard 1 Ampere or 5 Amperes for larger primary current ratings.
When a current is too high to measure directly or the voltage of the circuit is too high, a current transformer can be used to provide an isolated lower current in its secondary which is proportional to the current in the primary circuit. The induced secondary current is then suitable for measuring instruments or processing in electronic equipment. Current transformers also have little effect on the primary circuit. Often, in electronic equipment, the isolation between the primary and secondary circuit is the important characteristic.
Current transformers are used in electronic equipment and are widely used for metering and protective relays in the electrical power industry.
Like any transformer, a current transformer has a primary winding, a core and a secondary winding, although some transformers, including current transformers, use an air core. In principle, the only difference between a current transformer and a voltage transformer (normal type) is that the former is fed with a 'constant' current while the latter is fed with a 'constant' voltage, where 'constant' has the strict circuit theory meaning.
The alternating current in the primary produces an alternating magnetic field in the core, which then induces an alternating current in the secondary. The primary circuit is largely unaffected by the insertion of the CT. Accurate current transformers need close coupling between the primary and secondary to ensure that the secondary current is proportional to the primary current over a wide current range. The current in the secondary is the current in the primary (assuming a single turn primary) divided by the number of turns of the secondary.
Typically, current transformers consist of a silicon steel ring core wound with many turns of copper wire. The conductor carrying the primary current is then passed through the ring; the CT's primary therefore consists of a single 'turn'. The primary 'winding' may be a permanent part of the current transformer, with a heavy copper bar to carry current through the core. Window-type current transformers (aka zero sequence current transformers, or ZSCT) are also common, which can have circuit cables run through the middle of an opening in the core to provide a single-turn primary winding. To assist accuracy, the primary conductor should be central in aperture.
CTs are specified by their current ratio from primary to secondary. The rated secondary current is normally standardized at 1 or 5 amperes. For example, a 4000:5 CT secondary winding will supply an output current of 5 amperes when the primary winding current is 4000 amperes.
The AC Current Transformers (CT) for Electrical Meters market covers Pin, Wire, etc. The typical players include VAC, Falco Electronics, J&D Electronics, Shenke, etc.
According to the new market research report “Global AC Current Transformers (CT) for Electrical Meters Market Report 2023-2029”, published by QYResearch, the global AC Current Transformers (CT) for Electrical Meters market size is projected to reach USD 0.39 billion by 2029, at a CAGR of 3.7% during the forecast period.
Figure. Global AC Current Transformers (CT) for Electrical Meters Market Size (US$ Million), 2018-2029
Based on or includes research from QYResearch: Global AC Current Transformers (CT) for Electrical Meters Market Report 2023-2029.
Figure. Global AC Current Transformers (CT) for Electrical Meters Top 5 Players Ranking and Market Share（Based on data of 2021, Continually updated）
Based on or includes research from QYResearch: 2021 data information of Global AC Current Transformers (CT) for Electrical Meters Market Report 2023-2029.
The global key manufacturers of AC Current Transformers (CT) for Electrical Meters include Falco Electronics, Accuenergy, VAC, TE Connectivity, Nanjing Zeming Electronic, Hioki E.E., Flex-Core, Shenke, AutomationDirect, Omega Engineering, etc. In 2021, the global top five players had a share approximately 31.0% in terms of revenue.
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